WASHINGTON - US Defense Secretary Chuck Hagel ordered an aircraft carrier moved into the Gulf on Saturday, readying it in case Washington decides to pursue a military option after insurgents overwhelmed a string of Iraqi cities this week and threatened Baghdad.

"The order will provide the Commander-in-Chief additional flexibility should military options be required to protect American lives, citizens and interests in Iraq," the Pentagon said in a statement.

The carrier USS George HW Bush, moving from the North Arabian Sea, will be accompanied by the guided-missile cruiser USS Philippine Sea and the guided-missile destroyer USS Truxtun, the statement said. It added the ships were expected to complete their transit into the Gulf later on Saturday.